1. Field of the Invention
The present invention relates, generally to a dual clutch transmission and, more specifically, to a dual clutch transmission with radially nested clutches having a common disk carrier.
2. Description of the Related Art
Power shifting transmissions used in motor vehicles are employed to transfer power from the prime mover, or engine, to the driven wheels. Power shifting transmissions can take the form of a dual, or twin, clutch transmission where the torque input from the engine is delivered to two input shafts each supporting a portion of the gear sets. Each input shaft has an associated clutch to selectively transfer torque provided by the engine. Since the input engine torque comes through a single input member, such as the flywheel or crankshaft, one structural arrangement for the dual clutch assembly is to dispose the two clutch assemblies in a single radially nested arrangement. The dual clutch assembly is operatively disposed about the two input shafts, which are also in a co-axial and co-centric arrangement. To selectively engage and disengage their respective input shafts, the two clutches of the dual clutch transmission are each comprised of a set of clutch discs, also referred to as a clutch pack. The clutch packs each include one set of discs physically coupled to one of the input shafts and another set of discs physically coupled to the torque input member. The two sets of clutch discs in each clutch pack are alternately supported by inner and outer disc supports. The clutches are engaged by compressing the two sets of discs together against a fixed back plate.
The conventional structure of radially nested dual clutches comprises an outer clutch with an outer disk carrier supporting the outer disks of the outer clutch and an inner disk carrier supporting the inner disks of the outer clutch. An inner clutch is radially nested within the outer clutch and includes an outer disk carrier supporting the outer disks of the inner clutch and an inner disk carrier supporting the inner disks of the inner clutch. Each clutch comprises an actuating piston to cause the inner and outer disks of the respective clutch to frictionally engage each other and thereby transfer torque from the torque input member to the respective input shaft.
Each piston is axially movable and is guided by a corresponding radial cylinder. The cylinder and actuating piston form a pressure chamber, which can be pressurized by hydraulic fluid in order to bring the disks into (or if necessary out of) frictional engagement. Frequently, a compensating piston is additionally assigned to one or both actuating pistons. The actuating piston and the compensating piston form a compensating chamber. The compensating chamber can also be supplied with hydraulic fluid to compensate for an excess of pressure in the pressure chamber caused by centrifugal force, which occurs in the case of increasing speed. In most conventional designs, although radially nested, the two clutches are entirely separate and individually complete. In some variants, the compensating chamber of the outer clutch is formed by the actuating piston of the outer clutch and the outer disk carrier of the inner clutch.
Although the structure of the conventional dual clutches assemblies mentioned above is generally adequate for the intended purpose, they provide radially nested dual clutch assemblies that are needlessly complex and bulky. In the conventional designs, the clutch assemblies are separate each having inner and outer disk support carriers, inner and outer radial guide cylinders, inner and outer compensating pistons, and inner and outer actuating pistons. Thus, the size and weight of the conventional radially nested dual clutch assemblies cause parasitic losses that reduce the efficiency of the transmission and the vehicle. Further, the combination of the numerous nested components is difficult to assemble adding to its overall production costs.
Accordingly, there remains a need in the related art for a dual clutch transmission having a radially nested dual clutch assembly with fewer components, which allows for a lighter, more compact, and more efficient dual clutch assembly. There also remains a need for this type of transmission having a radially nested dual clutch assembly that provides greater efficiency, more cost effective production, and ease of assembly by employing fewer components.